Human brain functions are mostly studied using functional magnetic resonance imaging (fMRI). However, the application of this technology since the 1990s has led to seemingly contradictory notions regarding the large-scale functional organization of the human brain.
A collaborative team comprising scientists from Emory University, the University of California and Los Angeles (UCLA), the Montreal Neurological Institute, Vanderbilt University and the National University of Singapore bridged the gap between two broad categories of broad-based brain organization and demonstrated the most functional phenomena in the human brain that can be reduced to groups of three spatiotemporal patterns. . These patterns explain most of the brain’s global spatial structures responsible for the functional connectivity and consolidation of observations made with resting-state fMRI that were previously thought to be different.
“FMRI indicates that the brain has a globally coherent spatial structure, but there is still no consensus among scientists on the correct way to catalog this structure,” said Lucina Odin, PhD, professor of psychiatry and biobehavioral sciences and director of the Brain Communication and Cognition Laboratory at the Semel Institute. For Neuroscience and Human Behavior, “We’ve shown that a small number of spatiotemporal patterns can do the job.”
The results were published in an article titled “A scant description of global functional brain organization in three spatiotemporal patterns” in the journal natural neuroscience.
said Taylor Bolt, Ph.D., a statistician at UCLA Semel and first author of the paper.
MRI procedures are based on low-frequency spontaneous blood oxygenation level-dependent (BOLD) fluctuations. These fluctuating signals reflect synchronous neural activity between different brain regions and are organized into global patterns that span across functional systems of perception, cognition, and action. Spontaneous fluctuations have been subjected to increasingly complex analytical techniques, resulting in competing descriptions of large-scale functional brain organization.
These global patterns are categorized into two broad categories: zero synchronization and time delay. Zero delay synchronization represents “stationary waves” where there is instantaneous dependence between two signal cycles or no time delay between two BOLD signals. This can be visualized as the simultaneous synchronization of brain regions across the cortex. On the other hand, synchronization represents the time interval of “traveling waves” where the dependence between two signal cycles is separated by a delay.
To extract the traveling wave patterns, the authors applied PCA (principal component analysis) to complex BOLD signals, which were originally derived using a mathematical transformation technique.
There has been “little attempt to pool the results across different approaches,” the researchers said. Odi compared this lack of a unifying concept with an Indian proverb where blindfolded men facing different parts of the elephant arrive at different descriptions of the same animal.
The authors note: “We sought to unify the observed phenomena across these two categories in the form of three low-frequency spatiotemporal patterns consisting of a mixture of standing and traveling wave dynamics.”
The authors hypothesize that the stationary and moving wave representations capture different aspects of a small number of spatiotemporal patterns. In testing this hypothesis, the authors found that several previous observations, including functional connectivity gradients, positive/negative task-correlation patterns, temporal lag propagation patterns, and functional network structure, can be standardized in framework modeling. Both standing and traveling wave structures.
These findings present a global functional organization of the brain that could inspire investigations into coordinating principles of brain activity.
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